This invention relates to a disposable capsule filter, which is particularly suited to the filtering of paint, ink, etc. containing an organic solvent.
As a liquid filter for water as well as food and pharmaceutical products, etc., for increasing the speed of operation of replacing filter elements, disposable capsule filters as shown in FIG. 5 are extensively used, in which filter element 2 is set in advance in synthetic resin vessel 1 and is discarded together with vessel 1 when it is clogged.
However, filters for paints and varnish, particularly magnetic paint, inks, etc. can be only with difficultly be provided as disposable filter. This is so because such paints or the like contain a great quantity of strong organic solvent having a strong polarity. If a disposable capsule filter is used for such paint for long period of time, the vessel is gradually attacked by the organic solvent which may lead to its rupture with internal pressure increase and to subsequent possible fire hazards.
Further, paints and varnish, inks, etc. usually have a high viscosity, and their filtering inevitably dictates high pressure loss. For this reason, it is very difficult to maintain pressure resistance with the sole plastic material of the capsule portion. If it is intended to secure the pressure resistance with the sole plastic material, it is necessary to provide a very large thickness for the vessel. Such a vessel is economically very inadequate as so-called disposable filter. In order to solve this economical problem, the thickness of plastic vessel is reduced to a threshold thickness such that corrosive attack can be withstood, and for the purpose of increasing the pressure resistance, an upper metal holder is fitted on the plastic vessel and united with a lower metal holder with a V-band clamp when using the filter. It is well known in the art that among current techniques of plastic molding that injection molding is most inexpensive. However, with this molding technique, it is impossible to form a large swelled portion 11 as shown in FIG. 2. Therefore, as shown in FIG. 3, upper and lower vessel parts or halves 12 and 13 have to be independently injection molded and bonded together using supersonic waves or high frequency wave or heat. If a vessel formed in this way is used for filtering a fluid containing a strong solvent as base, a portion of the vessel, to which strong heat was given, i.e., a bonded portion having been deteriorated by oxidization, is strongly attacked by the solvent, and this will give rise to leakage in the use of the filter.
Instead of providing swelled portion 11 as shown in FIG. 3, it is conceivable to form as increased thickness portion 14 corresponding in position to a V-band clamp, as shown in FIG. 4. However, it is very common that such molding will produce a commonly termed sink mark in the local increased thickness portion 14, such a sink mark having to be removed by subsequent machining. Further, it is a most significant problem in this case that a plastic material capable of withstanding strong solvents, typically polypropyrene, is highly fragile, so that if a strong stress is produced in increased thickness portion 14 with a V-band clamp or the like, cracks may be formed which may cause bursting. For this reason, a vessel having a shape as shown in FIG. 4 is substantially practically infeasible.